1. Field of the Invention
The invention relates to a drive device for a motor vehicle part which can be adjusted between at least two positions and a process for adjusting a motor vehicle part between at least two positions.
2. Description of Related Art
DE 43 21 264 A1 discloses a drive device in which an electric motor drives a motor vehicle window pane. By means of two Hall sensors which are offset by 90 degrees and which interact with a magnet located on the motor shaft a signal is produced from which the instantaneous period duration of a motor revolution and thus the instantaneous motor rpm are determined at each time at which one such signal enters a control unit for controlling the motor. As soon as the instantaneous rpm change resulting from the difference of two successive rpm measured values exceeds a stipulated threshold value the motor is reversed in order to release a possibly pinched article.
DE 195 11 581 A1 discloses a similar drive device in which however the threshold value is variably chosen depending on the position, a memory for certain positions of the adjustment path storing the speed change acquired in an earlier run between two adjacent positions, in order to compute therefrom as a function of position depending on the last currently acquired position and speed the shut-off threshold for the speed.
DE-OS 29 26 938 discloses acquiring the motor rpm in a sliding roof drive at uniform time intervals, finding the differences of successive values, adding these differences to one another when they are larger than a predetermined threshold value, and triggering the shut-off or reversal of the motor as soon as the added sum exceeds a predetermined threshold value.
DE 43 12 865 A1 discloses a drive device for a motor vehicle window which acquires the motor rpm by means of two Hall detectors, and which when a threshold is exceeded for the relative change of rpm reverses the motor. In doing so the threshold value is continually recomputed depending on the acquired motor voltage and the ambient temperature which is determined by a temperature sensor on the motor. In doing so the status/operating times of the motor are considered in order to be able to draw conclusions about the ambient temperature from the motor temperature.
DE 196 18 219 A1 discloses determining the rpm threshold or the rpm change threshold of the motor, starting from which reversal of the motor takes place, from the position-dependent rpm data of a reference run which has taken place beforehand depending on the position of the cover for a sliding roof drive.
The defect in these drive devices which acquire the rpm is that between two signals for acquiring the period or the motor rpm the pinching protection is not effective and under certain circumstances pinching of an article is only recognized with a delay; this leads to an increased pinching force and thus to damage to the actuation mechanism of the adjustable motor vehicle part or to injury to pinched body parts.
DE 195 14 954 A1 discloses a drive device for a motor vehicle window which acquires the motor current and moreover acquires the window position by means of Hall sensors in the motor and when the threshold value is exceeded for the motor current as a function of the window position reverses the motor.
The disadvantage in these drive devices which acquire the motor current is that additional electronic components are necessary for acquiring the motor current.
The object of this invention is to devise a drive device for a motor vehicle part which can be moved between at least two positions and a process for adjusting a movable motor vehicle part between at least two positions, by which pinching of an article is prevented without additional components.
This object is achieved in accordance with the invention by a process and by a drive device as described below.
The object of this invention is to devise a drive device for a motor vehicle part which can be moved between at least two positions and a process for adjusting a movable motor vehicle part between at least two positions, by which prompt acquisition of pinching of an article is acquired without additional components.
This object is achieved as claimed in the invention by a process as claimed in claim 1 and by a drive device as claimed in claim 29.
In this approach in accordance with the invention, it is advantageous that by the pinching protection is also active between two signals, i.e., between two measured values, without additional cost, as is necessary, for example, in the motor current acquisition, and thus, can react very promptly to cases of pinching.
Preferably the extrapolation instants have a fixed time interval.
Preferably spring strengths, damping and friction of the drive device are considered in determining the action of the force. The triggering threshold can be placed lower by this modelling of the system.
Furthermore, it is preferably provided that the estimated rpm change results from the difference of the period duration estimated for the extrapolation instant and the period duration estimated for the preceding extrapolation instant, the period duration which has been estimated for each extrapolation instant resulting as the sum from the last measured period duration and the parameter-weighted sum of several period durations measured before the last measured period duration, the latter sum being multiplied by the time which has passed since the last measurement.
Preferably only the last three of the measured values of the period duration preceding the last measurement before the extrapolation instant are considered. This is sufficient for satisfactory function.
Preferably the force acting on the motor vehicle part is determined by each estimated rpm change being multiplied by a proportionality factor and the values obtained in this way being added up as soon as the estimated rpm change exceeds a lower threshold value. In this way the effect of small rpm changes is reduced; this increases the triggering accuracy.
In the preferred embodiment of the invention it is furthermore provided that when the estimated rpm change exceeds an upper threshold value, instead of the estimated rpm change only the upper threshold value becomes part of the summation. In this way faulty triggering of the pinching protection by the effects of vibration is prevented.
The upper threshold value is chosen preferably differently depending on the last determined rpm change value. In this way the triggering accuracy can be further increased.
Furthermore the control unit is preferably made such that the proportionality factor for determining the force change from the rpm change is chosen depending on the motor characteristic which is determined before start-up without the driven motor vehicle part for at least one motor voltage. In this way better modelling of the individual system is achieved so that the triggering threshold can be set lower.
One advantageous development furthermore consists in that parallel to determining the estimated value of the current action of force in at least one second independent computation from the acquired pulse signals at certain second instants a second value for the current force action on the motor vehicle part is determined, the second value being used as an additional criterion in the decision whether the motor is turned off or reversed or not. This has the advantage that the first and the second computation can be optimized for pinching processes or force changes of different speeds; this further increases the triggering accuracy.
Preferably at certain times spectral analysis of the rpm changes estimated or determined within a certain time window up to the analysis point is done, the motor only being turned off or reversed when the determined spectrum meets certain requirements. This protects against faulty triggering under conditions of vibration.